A magnetic circuit component including a magnetic core made of a soft magnetic material, such as iron or an iron alloy, and a coil arranged around the magnetic core is utilized in various fields. On example of constituent elements of the magnetic core is a compact. The compact is typically manufactured by filling material powder made of a soft magnetic material, into a molding space, which is defined by a die having a through-hole and a lower punch arranged to close one opening of the through-hole of the die, and then compression-molding the material powder by an upper punch and the lower punch. A compression-molded product drawn out from the die is usually subjected to heat treatment aiming at removal of distortion, etc.
When the above-mentioned magnetic circuit component is used in an alternating current (AC) magnetic field, an iron loss (generally given as the sum of a hysteresis loss and an eddy current loss) occurs in the magnetic core. In particular, when the magnetic circuit component is used at high frequencies of several kHz or higher, the eddy current loss is significantly increased. Therefore, reduction of the eddy current loss is demanded in the magnetic core. In order to reduce the eddy current loss, it is proposed to employ, as material powder, coated powder formed of a metal particle made of a soft magnetic material, such as an iron particle, and covered with an insulating coating over its outer peripheral surface, thus increasing electrical resistance (see Patent Literature (PTL) 1). It is also proposed to perform post-treatment, such as acid treatment, on a compression-molded product to remove a portion (hereinafter called a “bridge portion”) where the insulating coatings are damaged due to, e.g., sliding contact between the compression-molded product and an inner peripheral surface of a die and an electrically conductive state is generated because the metal particles are exposed from the insulating coatings and are deformed to come into contact with each other (see PTL 1).